1. Field of the Invention
The present invention relates to a carrier substrate and a method for manufacturing the carrier substrate, and particularly to a carrier substrate having a multiple layers therein, in which a trace is directly connected to a via without using a capture ring, and a method for manufacturing the carrier substrate.
2. The Prior Arts
As the trend of compactness and lightness of electronic products and the continuously increasing demand of function, a chip used in the electronic products has a rapidly increasing number of I/O pins and packaging technology therefore is becoming more demanding. As to the packaging technology, a flip-chip technology has been widely utilized and a packaging density thereof also has a constantly rapid growth, from 90 nm to 65 nm and even to 45 nm. Meanwhile, there is a demand for a thinner wire on an IC carrier substrate, i.e. a width of the wire has to be considerably reduced from 50 μm to 20 μm (with a corresponding pitch of 40 μm) or even to 15 μm (with a corresponding pitch of 30 μm).
The IC carrier substrate has a multi-layer structure. In forming such IC carrier substrate, a build-up process is generally used to fabricate each of the multiple layers. To connect different layers there between, a blind hole is formed and processed by laser and a copper electroplating process is generally involved. According to some general design criterions, an annular ring made of metal is generally formed on a circumference of the blind hole for the following reasons. The first one is to avoid an attack on copper on a wall of the blind hole from an etchant when a wire is etched by using the etchant, which causes the copper electroplated layer to have an insufficient thickness and thus an open circuiting. The second one is to prevent a photoresist from covering the blind hole when the electroplating process according to a pattern is being undertaken, so that the electroplating process is not adversely affected. To determine a dimension of the annular ring, what an alignment extent can be achieved up to in the manufacturing process has to be considered. However, the annular ring on a fine via in between two adjacent layers in the carrier substrate is difficult to be reduced from 50 μm to 30 μm in diameter. Due to a trend of provision of an increased wiring density, the dimension of the annular ring has to be reduced, so that the pitch between wires in the carrier substrate can also be reduced to obtain an increased wiring density, wire width, or reduced carrier substrate dimension and reduced number of the build-up layers. However, the reduction of dimension of the annular ring has a limit since an alignment error may unavoidably present in the processing apparatus. Currently, the annular ring is generally designed to have a dimension of about 20 μm one side, which takes up a significant space and thus brings about an additional limit on other elements in the carrier substrate. Although the capture ring may be reduced in dimension as the alignment precision of the manufacturing apparatus is improved or a more complicated process is introduced, the cost is correspondingly increased.
To overcome the aforementioned problems, a ringless design has been suggested for the multi-layer structure. In this manner, the wiring density can be effectively increased since the annular ring is no longer to be considered, which also results in a decreased footprint. However, since the finer wires would have a considerably reduced adhesion and strength with the carrier substrate, reliability of the carrier substrate may become another problem. In this regard, there is a need for a new carrier substrate structure and a method for manufacturing the same.